1. Field of the Invention
The present invention relates to a control system and, more particularly, to a control system capable of specifying a mixture route of noise which is mixed into daisy-chained input/output units.
2. Description of the Related Art
In a control system where a controller and input/output units are daisy-chained through serial communication, external noise is a factor causing communication failure between devices. In particular, in a control system used in an FA environment such as a factory, in many cases, the external noise causes communication failure, and thus, the countermeasures are required. With respect to the communication failure caused by the external noise, since it is difficult to specify a noise mixture route, in many cases, the cause cannot be specified, or it takes a long period of time to investigate the cause. Therefore, in order to solve the problem early, it is important to determine the noise mixture route.
In the related art, Japanese Patent Application Laid-Open No. 2011-103545 discloses a technique where external noise detection units are connected to a plurality of circuits into which external noise is expected to be mixed, data detected by the external noise detection units is stored in a recording unit, and type and mixture route of noise are specified by comparing the stored data with data of a normal period.
However, for applying the above technique, since the detection circuits are necessarily connected to all the external noise mixture routes, in general, circuit size is also increased, and thus, there is a problem in that the cost is increased.
In addition, Japanese Patent Application Laid-Open No. 2010-004144 discloses a controller having a serial communication function including a phase detection circuit outputting a phase difference between a phase of a rising or falling edge of serial data caused by external noise or the like and a phase of a reference clock as phase data.
However, in the above-described controller, although the occurrence of invasion of the external noise can be sensed by detecting the phase difference caused by the external noise, the external noise mixture route cannot be specified.